1. Field of the Invention
The present invention relates in general to doubling the number of scanning line of a television signal in a television (TV) of the interlaced scanning type, and more particularly to an apparatus for interpolating scanning lines of a TV signal in a TV, which is useful in removing step edges of a video which has a diagonal variation in the case of using conventional line repetition and vertical average methods.
2. Description of the Prior Art
Generally, in a TV of the interlaced scanning type, a line structure, a line flicker, a vertical resolution insufficiency and etc. are generated as picture quality degradation elements due to the interlaced scanning. For this reason, for the purpose of solutions to these problems, there has conventionally been employed a method of scanning an interpolation scanning line between scanning lines to double the number of the scanning lines. The conventional method of doubling the number of the scanning lines includes an intrafield interpolation method which is classified into a line repetition method of performing the interpolation using the previous scanning line as the interpolation scanning line and a vertical average method of performing the interpolation by averaging the upper and lower scanning lines with respect to a scanning line to be interpolated, and an inter-field interpolation method of interpolating a scanning line of the previous field as the interpolation scanning line.
Referring to FIGS. 1A to 1D, there are shown block diagrams arc) views illustrating the conventional intra-field interpolation method, respectively. FIG. 1A is a block diagram of an intra-field interpolator using the line repetition and FIG. 1B is a view illustrating the intra-field interpolation method using the line repetition. In FIG. 1A, the intra-field interpolator comprises a one line memory 1 for delaying a received video signal Yin of a television signal by one line, a first time compressor 2 for compressing the time of an output signal from the one line memory 1 by 2 to 1, a second time compressor 3 for compressing the time of the video signal Yin by 2 to 1, and a switch SW1 for selectively outputting one of output signals from the first and second time compressors 2 and 3.
FIG. 1C is a block diagram of an intra-field interpolator using the vertical average and FIG. 1D is 8 view illustrating the intra-field interpolation method using the vertical average. In FIG. 1C, the intra-field interpolator comprises a one line memory 4 for delaying a received video signal Yin of a television signal by one line, an adder 5 for adding an output signal from the one line memory 4 to the video signal Yin, a 1/2 amplifier 6 for amplifying an output signal from the adder 5 by a 1/2 level, a first time compressor 7 for compressing the time of an output signal from the 1/2 amplifier 6 by 2 to 1, a second time compressor 8 for compressing the time of the video signal Yin by 2 to 1, and a switch SW2 for selectively outputting one of output signals from the first and second time compressors 7 and 8.
Referring to FIGS. 2A and 2B, there are shown a block diagram and a view illustrating the conventional inter-field interpolation method, respectively, FIG. 2A is a block diagram of an inter-field interpolator and FIG. 2B is a view illustrating the inter-field interpolation method. In FIG. 2A, the inter-field interpolator comprises a one field memory 9 for delaying a received video signal Yin of a television signal by one field, a first time compressor 10 for compressing the time of an output signal from the one field memory 9 by 2 to 1, a second time compressor 11 for compressing the time of the video signal Yin by 2 to 1, and a switch SW3 for selectively outputting one of output signals from the first and second time compressors 10 and 11.
The operations of the constructions in FIGS. 1A, 1C and 2A will hereinafter be described with reference to FIGS. 1B, 1D and 2B, respectively.
In FIG. 1B, a scanning line i to be interpolated is substituted by the previous line. Namely, the time of the video signal Yin delayed by the one line memory 1 is compressed by 2 to 1 by the first time compressor 2 and the time of the original video signal Yin is compressed by 2 to 1 by the second time compressor 3. As a result, the first switch SW1 selects the output signal from the first time compressor 2 with respect to the scanning line to be interpolated and selects the output signal from the second time compressor 3 with respect to the original scanning line. At this time, a switching clock of the first switch SW1 is half a period of one scanning line of the inputted signal,
In FIG. 1D, the scanning line i to be interpolated is substituted by averaging the upper and lower scanning lines a and b about the scanning line i in the field. Namely, the video signal Yin delayed by the one line memory 4 to added to the original video signal Yin by the adder 5 and then amplified by the 1/2 amplifier 6. The time of the output signal from the 1/2 amplifier 6 is compressed by 2 to 1 by the first time compressor 7 and the time of the original video signal Yin is compressed by 2 to 1 by the second time compressor 8. As a result, in a similar manner to that mentioned above with reference to FIG. 1A, the switch SW2 selects the output signal from the first time compressor 7 with respect to the scanning line to be interpolated and selects the output signal from the second time compressor 8 with respect to the original scanning line.
In FIG. 2B, the scanning line i to be interpolated is substituted by a scanning line of the previous field. Namely, the time of the video signal Yin delayed by the one field memory 9 is compressed by 2 to 1 by the first time compressor 10 and the time of the original video signal Yin is compressed by 2 to 1 by the second time compressor 11. As s result, the third switch SW3 selects the output signal from the first time compressor 10 with respect to the scanning line to be interpolated and selects the output signal from the second time compressor 11 with respect to the original scanning line.
However, the above-mentioned conventional interpolation methods have disadvantages as shown in FIGS. 3B to 3D. FIG. 3A is a waveform diagram illustrating a motion of the original video in one field. The reference numeral a represents a still video, the reference numeral b represents the video moved by one sample to the right, the reference numeral c represents the video moved by one sample upward and the reference numeral d represents the video moved by one sample diagonally. FIG. 3B is a waveform diagram illustrating the interpolation result which is obtained by utilizing the line repetition. From FIG. 3B, it can be seen that many step edges appear at the still video and the video of slow motion. FIG. 3C is a waveform diagram illustrating the interpolation result which is obtained by utilizing the line average or the vertical average. It can be seen from FIG. 3C that blurred edge portions appear at the still video and the video of slow motion. FIG. 3D is a waveform diagram illustrating the interpolation result which is obtained by utilizing the interfield interpolation. Herein, the interpolation is accurately performed at the still video, but inaccurately at the moved video.